Quote: You know sancho if you would use your vast knowledge of polygraph and please explain how a truthful person fails a polygraph
OK pay attention. ANY scientific test by definition must have an error rate. If there is no error rate it cannot be called a scientific test. Scientific tests have accuracy rates and error rates. Accuracy Rate is what you have left after you subtract the error rate from 100% .Error rates are made up of False Positives and False Negatives. In Polygraph a False Positive is where the results of the examination indicate deception when the subject is telling the truth. A False Negative in Polygraph means that the results indicate truthfulness when the subject was in fact lying regarding a relevant issue. If you add the number of false positives to the number of false negatives and calculate the total as a percentage of the tests in a given group, you have the error rate.
Generally in polygraph there are 3 possible results for examinations. Deception Indicated, No Deception Indicated and Inconclusive. Inconclusive results are not part of the error rate. Inconclusive just means that the data was unsuitable for evaluation. The NAS study said that more research needed to be done to quantify the error rate in polygraph. They said the same thing when they reviewed DNA research.
I can't tell you every possible thing that could cause an error in a polygraph test any more than you could tell me every possible thing that could cause an error in a DNA comparison. From the literature I have read, polygraphists shouldn't do an exam after an aggressive interrogation due to the possibility of physiological exhaustion causing an error, they don't permit extra people in the polygraph room in order to avoid errors caused by distraction due to talking or movement of the 3rd party, they don't test people with recent injuries to avoid errors caused by chronic pain and they don't conduct tests on people unable to comprehend the meaning of questions to avoid errors caused by misunderstanding the meaning of a question, etc. I can't name them all but errors do occur. If you look at other scientific tests you would discover that many have a much higher error rate than any quantified by known studies for polygraph. A TB skin test for example has an error rate between 30 and 70%.
Error rates cannot be affected from within a testing protocol. If you change your scoring/evaluation criteria to reduce false positives, false negatives will increase proportionately. Error rates can only be changed by altering the protocol in some fashion.
Since all scientific tests have error rates, necessarily forensic examinations used by the police also have error rates and a false positive in any of them could put a suspect in exactly the same predicament as a false positive in a polygraph test.
This includes but isn’t limited to:
Latent Fingerprint comparison: The FBI AFIS system sometimes provides dozens of probable matches that require further investigation. Sometimes it only kicks out one match and it’s the wrong guy. Why? I don’t know. Do you?
I won’t do that with the rest but they all have error rates
Blood Alcohol Analysis (Breath)
Blood Alcohol Analysis (Blood)
Handwriting Comparison
Statement Analysis
Determination of speed from skid marks
Determination of speed from yaw marks
Determination of speed from deformation of metal
Presence of blood
Presence of human blood
Marijuana field test
Marijuana Lab test
Heroin Field test
Heroin Lab Test
as a matter of fact to save time all presumptive tests for drugs whether in the field or lab have error rates.
Urinalysis
Ink analysis
Identification of trace evidence
Foot Print Comparison
Puzzle fit analysis
Ballistics
Hair Analysis
I still stand by my previous post that if you took all of the people who have posted on this board during the last 8 years whining that they told the truth and failed their polygraph and added them to the 1325 signatures including Joke Names, Duplications and Line Voided, during that same time period, and compared them to the number of polygraph tests administered during that same time period, you would find that you are a member of a very tiny yet vocal group, even if you assume that every one of your number is the victim of some error.
I would argue that if every one of you were found to have some error on your polygraph you couldn't successfully invalidate the 98% accuracy rate claim that Jack Trimarco allegedly made to Dr. Maschke regarding polygraph.
While an error in your particular case may be significant to you because of your personal involvement, the mere possibility that an error was made in your case is not that significant to the big picture.
Do you really think your interrogation would have been any less traumatic if you didn’t take a polygraph and the investigator decided you were the culprit? You just decided to focus on polygraph as the source of your discomfort when it was the interviewer that made you feel bad.
I don't know of anyone who has ever been convicted of a crime based solely on the results of a polygraph, but a blanket statement that they cannot be admitted as evidence is innacurate.
Sancho Panza The character was the voice of reason in the face of insanity.